The present invention relates to a turbine, and in particular to a turbine which can be used in a turbocharger comprising a turbine stage and a compressor stage on a common shaft.
In known turbochargers, the turbine stage comprises a turbine wheel, a housing (which may comprise several components) in which the wheel is mounted between an inlet and an outlet defined by the housing, and an array of vanes mounted in the inlet so as to direct gas towards the turbine wheel. It has been known for many years that advantages can be obtained if the turbine stage has a variable flow size, that is a variable inlet cross-section which can be controlled to optimise flow velocities despite variations in mass flow rates.
One widely applied method of varying the flow size of a turbocharger turbine stage is to provide an array of movable vanes in the turbine inlet. Each vane can pivot about an axis extending across the inlet parallel to the turbocharger shaft and aligned with a point approximately half way along the vane length. A vane actuating mechanism is provided which is linked to each of the vanes and is displaceable in a manner which causes each of the vanes to move in unison, such a movement enabling the cross sectional area available for the incoming gas and the angle of approach of the gas to the turbine wheel to be controlled. Such arrangements are generally referred to as swing vane variable geometry turbochargers.
In swing vane turbochargers typically each vane is mounted on a pivot axle, the axle projecting through a wall of the inlet and supporting outside the inlet a crank or lever. The crank of each vane is coupled to an actuator ring which extends around the turbocharger housing generally outside the inlet but adjacent the vane cranks. This actuator ring is generally referred to as a unison ring. The unison ring is coupled either directly to the vane cranks or by links which provide for relative movement between interconnected components. Typically the links are pivotally connected to the vane cranks. Manufacturing considerations mean that there must be clearance at such interconnections and this clearance results in backlash in the mechanism and vibration of the interconnected parts. The temperature of the exhaust gases in which turbocharger turbines operate is such that conventional lubricants are not effective and as a result wear inevitably takes place even if special materials are used. Such wear is detrimental to the performance and controllability of the turbine and hence to the performance of an engine to which the turbocharger is attached. Wear of each individual part in the mechanical chain accumulates such that after the mechanism has been in use for some time backlash in the mechanism can lead to loss of control and possible even total failure.
It is an object of the present invention to obviate or mitigate the problems outlined above.
According to a first aspect of the present invention, there is provided a turbine comprising a turbine wheel, a housing in which the wheel is mounted between an inlet and an outlet defined by the housing, a plurality of vanes rotatably mounted in the inlet, and an actuator which is displaceable relative to the vanes and is coupled to each vane such that displacement of the actuator causes the vanes to pivot, wherein each vane is coupled to the actuator by a respective flexible link arranged such that actuator displacement causes the links to flex.
The flexibility of the links enables rotation of the vanes as a result of actuator displacement to be accommodated by flexing the links, enabling the use of connections between the links and the vanes which are not subject to backlash.
According to a second aspect of the present invention, there is provided a turbine comprising a turbine wheel, a housing in which the wheel is mounted between an inlet and an outlet defined by the housing, a plurality of vanes rotatably mounted in the inlet, and an actuator which is displaceable relative to the vanes and is coupled to each vane such that displacement of the actuator causes the vanes to pivot, each vane being coupled to the actuator by a respective flexible link arranged such that actuator displacement causes the links to flex, wherein each link has one end secured to the respective vane in a manner which prevents relative movement between the vane and said one end and an other end secured to the actuator in a manner which prevents relative movement between the actuator and said other end.
Similar connections may be used at the ends of the links connected to the actuator. The links may be secured in position by any convenient means which prevents relative movement between the ends of the links and the vane and/or the actuator. For example the links may be secured by rivets or by being received in appropriate slots. As in such arrangements there is no rubbing and hence wear between the various components, long term reliability is enhanced.
Each link preferably flexes in a direction lying in a plane plane perpendicular to the rotational axis of the respective vane.
Each vane may be supported and axially connected to a crank, each vane crank being coupled to a respective link. The actuator may be defined by a ring extending around the housing adjacent to the vanes outside the inlet, the links extending between the actuator ring and the vane cranks.